(1) Field of the Invention
The present invention relates to a light-emitting device on which semiconductor light-emitting elements are mounted and a manufacturing method of such a device.
(2) Description of Related Art
Conventionally, a light-emitting device on which semiconductor light-emitting elements, such as light-emitting diodes (LEDs) and laser diodes (LDs), are mounted is sometimes provided with an optical member, such as a wavelength conversion member and a lens, that is made in contact with the semiconductor light-emitting element, in order to extract light having desired optical characteristics, such as a wavelength and the like. In the light-emitting device of this type, a composite oxide or nitride, such as a YAG-based phosphor, or a translucent resin to which the phosphor is ground into powder and added, and is adopted as, for example, the wavelength conversion member.
In the semiconductor light-emitting element, in contrast to the fact that a nitride-based semiconductor forming the semiconductor light-emitting element and a substrate made of sapphire or the like for use in forming the nitride-based semiconductor are materials having a high refractive index, the translucent resin generally has a low refractive index and also has a high thermal expansion coefficient. For this reason, the light-emitting device, which is provided with an optical member made of the translucent resin of this type, tends to cause light released from the semiconductor light-emitting element to be easily reflected by the interface with the optical member, which lowers the light extraction efficiency. In addition, separation between the optical member and the semiconductor light-emitting element might occurs due to a difference between their thermal expansion coefficients. Moreover, since the resin has a low thermal conductivity, its heat radiating characteristic is inferior. In contrast, inorganic materials, such as ceramics, have thermal expansion coefficients close to those of the semiconductor light-emitting elements in comparison with the resin, so that selection can be properly made among materials having a high thermal conductivity or a high refractive index. However, in the light-emitting device, the optical member made of the inorganic material is normally installed as such a member preliminarily molded into a plate shape and bonded to the semiconductor light-emitting element, and for this reason, a layer of an adhesive agent made of a translucent resin is interpolated in a gap to the semiconductor light-emitting element.
Therefore, a method has been developed by which the optical member made of an organic material is bonded to the semiconductor light-emitting element without using an adhesive agent. For example, JP-A No. 2006-352085 has disclosed a light-emitting device in which a core generation layer is formed on the rear surface of a substrate prior to a formation of the semiconductor light-emitting element, with the core generation layer being thermally press-bonded to a ceramic material. However, in the bonding method described in JP-A No. 2006-352085, since the press-bonding process is carried out at a high temperature of about 200 to 500° C., the semiconductor light-emitting element tends to be deteriorated, or a press-bonding process at a low temperature fails to carry out a firm bonding process to sometimes cause separation.
Moreover, as a bonding method without requiring a high-temperature process, the inventors of the present application have developed a light-emitting device in which, by using a surface activation bonding process, a wavelength conversion member made of an inorganic material, such as YAG, is bonded to a sapphire substrate of a semiconductor light-emitting element (see International Publication No. 2011/126000).
On the other hand, in a semiconductor element (semiconductor device), a bonding method at a low temperature has been developed so as to bond a wafer on which the semiconductor elements have been formed to another wafer or the like. For example, in JP-A Nos. 2010-46696, 2011-235300 and 2012-223792 and T. Shimatsu, M. Uomoto, “Atomic diffusion bonding of wafers with thin nanocrystalline metal films”, Journal of Vacuum Science & Technology B Volume 28, Issue 4, p. 706, 2010, a technique has been disclosed in which two members, such as wafers, are firmly bonded to each other at room temperature by using an atomic diffusion bonding process.